This application is the national phase of international application PCT/JP99/03876 filed Jul. 19, 1999 which designated the U.S.
1. Technical Field
This invention relates to a spinning processing method, and more particularly to a spinning processing method in which a metal tube is drawn to form a section of reduced diameter and an apparatus therefor.
2. Background Art
A spinning processing method in which a steel tube is necking-processed to form a section of reduced diameter is disclosed in Japanese Patent Post-Exam. Publication No. H4-46647. According to this method, as shown in FIGS. 4 and 5, a plurality of forming rollers 103 are arranged around a steel tube 102, which is held by chuck 101, and the forming rollers 103 are rotated round the stationary steel tube 102 in the direction of an arrow C in FIG. 5. These rollers 103 are fed in the direction E along the tube axis, while being moved in the radially inward direction D of the steel tube 102, to form a section 104 of reduced diameter.
Another spinning processing method is disclosed in Japanese Patent Application Laid-Open Publication No. H10-24323. This method, contrarily to the above, rotates not forming rollers but a steel tube round its axis to perform the forming.
By the way, there are cases where, due to demands from the standpoint of manufacture, processing speed is required to be increased to thereby shorten processing time. In a spinning processing method, a processing speed is determined more by a rotating speed than by a feeding speed. In order to increase the processing speed, in the conventional methods wherein either a metal tube as the work or forming rollers are rotated, it is necessary to increase the rotating speed of the metallic tube or the forming rollers.
The present inventors have found that it is difficult to greatly reduce a processing time in the conventional spinning processing methods. This is because that even if intending to increase the rotating speed of the work or the forming rollers, because the rotational inertia of a chucking mechanism or a forming roller driving mechanism is large, it is impossible to greatly increase the rotating speed.
In particular, in the conventional spinning processing method which rotates the forming rollers round the work, the roller driving mechanism is relatively complicated and heavy, thereby making the inertia problems serious. Furthermore, the rollers will be subjected to a larger centrifugal force as their rotating speed increases, which prevents their motion in the forming direction, i.e., the radially inward direction of the work. For these reasons, not only the rotating speed of the forming rollers can not be increased greatly, but also some measures are required against the increase of the centrifugal force to thereby inevitably increase the cost of the forming machine.
It is an object of the present invention to provide a method of spinning processing which solves the above problems and increases the relative rotation speed between a work and forming rollers to greatly reduce processing time.
Another object of the invention is to provide a spinning processing apparatus which can carry out the above method.
The spinning processing method of the invention comprises the steps of rotating a metal tube round its longitudinal axis, rotating a plurality of forming rollers round the axis of the metal tube in the direction opposite to the metal tube, which rollers are arranged around the metal tube, moving the forming rollers towards the axis of the metal tube into pressure contact with the metal tube while moving the forming rollers in the axial direction of the metal tube relatively thereto to draw the metal tube to form a section of reduced diameter.
In the spinning processing method of the invention, since both the metal tube as the work and the forming rollers are rotated in the opposite directions to each other, the relative rotation speed between them comes to be high. For example, when setting the rotating speeds of the metal tube and the forming rollers identical, the relative rotation speed becomes twice.
The metal tube and the forming rollers, however, are not necessarily rotated at the same speed, and they may be rotated at different rotating speeds.
Furthermore, the relative movement between the forming rollers and the metal tube can be achieved by moving the rollers themselves, or the metal tube to the contrary, or both of them in the axial direction. Moving the metal tube alone allows the relative movement in the axial direction to be done easily and quickly as compared with the case where the relatively heavier forming roller driving mechanism is moved. On the other hand, in the arrangement wherein the forming rollers are moved, an automatic work exchanging mechanism is set up more easily, because the metal tube is stationary in the axial direction. Moving both the work and the forming rollers increases the relative movement speed between them and hence the feeding rate per time.
The spinning processing apparatus according to another aspect of the invention comprises means for supporting and rotating a metal tube round its longitudinal axis, a plurality of forming rollers arranged around the metal tube, means for rotating the forming rollers round the metal tube axis in the opposite direction to the metal tube, means for moving the forming rollers towards the metal tube axis into pressure contact with the metal tube, and means for moving the forming rollers relatively to the metal tube.
With this apparatus, the processing method of the invention described above can be carried out.